Bearings and bearing housing seals may be responsible for the majority of rotating equipment failures. There is a close relationship between the lives of these two critical components. The failure of a bearing housing seal may cause the bearings to fail and poor bearing conditions can reduce rotating equipment life. It is estimated that a small number of bearings achieve their minimum design life of from 24,000 to 40,000 hours (3 to 5 years). Rain, product leakage, debris, and wash-down water entering the bearing housing may contaminate the bearing lubricant and have a catastrophic effect on bearing life. Very small amounts of water can compromise bearing life. A contamination level of 0.002% water in the lubricating oil can reduce bearing life by as much as 48%. As little as 0.10% water is reported to reduce bearing life by as much as 90%.
Auxiliary mechanical equipment shaft seals, sometimes called bearing isolators or sealing rings, have become increasingly important to modern mechanical equipment, especially for equipment called upon to operate in hostile applications. For example, mechanical power transmission units used in rock quarries are often subjected to highly abrasive dust particles. Elastomeric lip or O-ring shaft seals can quickly wear out and fail in environments such as these. Dust and exterior contaminants cannot be excluded from the interior of the transmission housing by a failed standard sealing device. Nor can oil or other fluids be prevented from leaking out of the transmission devices past a worn lip seal.
To prevent the ingress of corruption and the egress of lubricating fluids, a number of auxiliary or improved primary sealing arrangements and devices have been provided. Some of these sealing devices provide a physical engagement of the shaft and a wiping action while the shaft operates. Other devices provide an interengagement and wiping action between seal parts. But in both such arrangements, the inevitable friction causes inevitable part wear.
For example, lip seals, commonly known as oil seals, are a well-established method of protecting bearing housings from water, dust, chemical or steam contamination. Lip seals normally involve a stationary elastomeric lip or lips touching the rotating shaft or sleeve at an angle so that contaminants are excluded from the housing. While lip seals have a low initial cost, lip seals have a short protection life, approximately 3,000 hours, due to wear of the elastomer or the shaft itself.
Another type of seal is a labyrinth device that contains a tortuous path that makes it difficult for contaminants to enter the bearing housing to degrade lubricant effectiveness. The advantages of labyrinths are their non-wearing and self-venting features.
Some of these commercially successful seal devices do not require any actual physical interengagement of the sealing member parts. Among such devices that have met with considerable commercial acceptance are those disclosed in U.S. Pat. Nos. 4,706,968; 4,466,620; 4,175,752; 4,114,902; 4,022,479; and 4,832,350.